Rotatable concrete mixing drum with improved discharge performance



2,883,166 ROTATABLE CONCRETE MIXING DRUM WITH IMPROVED R m7 E m M m. E M% K m L Ed H G0 M G mm L BF D April 21, 1959 LOU IS, G. HILKEMEIER I INVENTOR.

I BY M )4 United States Patent 2 Claims. (Cl. 259-161) This invention relates to an improved inclined rotatable mixing drum of the type used in transit concrete mixers,

and more particularly to a mixing drum of this type having a new and novel shape which enables the concreteto be discharged therefiom at a faster and thus more satisfactory rate.

Numerous attempts have been made, and are still being made, to increase the mixing drum discharge rate so that the time consumed by this operation is lessened, and the transit mixer thereby capable of making more trips during the course of a days operation. These attempts have resulted in proposals of what can be termed dischargeaiding devices, as for example, the vibration elements taught in application Serial No. 669,382, filed July 1, 1957 by the present inventor, and the frustoconical member taught in US. Patent 2,805,053 issued on September 3, 1957, each of which serves to facilitate drum discharge.

While these discharge aiding devices to a large degree solve this vexing problem, their application to mixing drums having the traditional frusto-conical shape from front end to rear discharge end, as is currently the universal practice, is an unfortunate contradiction as well as a needless limitation to their maximum operating po tential, for this said traditional frusto-conical drum shape is itself a major factor contributing to clogging in the discharging concrete, and thus to the slow, unsatisfactory discharge rate of the drum.

Undoubtedly this shape for the drum is being perpetuated by a desire to have, on the one hand, a maximum capacity interior mixing area, and on the other hand, a shape least susceptible to spillage. However, I have found that without resorting to any discharge aiding devices, but only by departing from this traditional shape universally applied to mixing drums, that a drum can be produced which has an acceptable high capacity-low spillage characteristic, and at the same time a faster and completely satisfactory discharge rate.

With the specific object in mind of improving the discharge rate of the inclined rotatable type concrete mixing drum, I therefore propose herein a new and novel conical in shape from its front end for only a prescribed portion of its axial length, and then be completed by a substantially cylindrical section which has the drum discharge opening provided in its remote end. In this shape, the drum has an acceptable high capacity-low spillage characteristic by reason of the front frusto-conical drum section, and in addition when the concrete flows to discharge through the said rear cylindrical drum section, there is no squeezing of and consequent clogging in the concrete as occurs in present drums, where the rear drum portion is frusto-conical and thus has a progressively narrowing passageway to the drum discharge opening.

This improved shape for inclined rotatable concrete Patented Apr. 21, 1959 mixing drums will be better understood from the accompanying specification and the single figure drawing form ing a part thereof, in which there is shown a partly broken away side view of this type of concrete mixing drum having this improved shape.

In the drawing, the rotatable mixing drum 1 is shown in the inclined angular position it would occupy when mounted on a transit concrete mixer. The mobile unit or truck, mounting frame, means for rotatably mounting the drum, driving means to rotate the drum in the directions for mix and discharge indicatedin the drawing, and other associated equipment such as discharging chutes have been omitted from the drawing since they do not form an essential part of the present invention. As has been indicated, the present invention concerns only an improved shape for the drum, which shape more particularly permits a faster rate of discharge than is possible using the completely frusto-conical shape now being almost universally employed in the concrete mixing art.

To apply this improved shape to the drum 1, the said drum is formed in two sections; a front section 2 and a rear section 3. These two sections are connected end-toend to each other at the point indicated at 4, the connection being accomplished by any well known manner, such as by welding; A discharge opening 5 for the drum 1 is provided inthe end of the rear drum section 3, and axially spiraled mixing blades 6, 7 originating in this said opening are mounted on the interior walls of the connected drum sections 2 and 3 extending the entire axial length of the drum 1.

Referring specifically to the shapes of the respective drum sections: the front section or section 2 is generally frusto-conical, and as such provides the drum 1 with an interior mixing area which has an acceptable high capacity-low spillage characteristic; and the rear section or section 3 is generally cylindrical, and as such provides the drum 1 with a wall parallel to the drum axis from the mixing area of the front drum section 2 to the drum discharge opening 5 in the end of the rear drum section 3.

To facilitate in the charging of the drum 1, and to increase the load carrying capacity thereof, a charging cone 10 is suitably welded centrally of the first turns of the mixing blades 6, 7 in the drum discharge opening 5. According to the well known operation of this charging cone 10, materials are inserted into the drum through the charging cone axial opening 11 which permits bypassing the first coils of the mixing blades 6, 7 and thus a faster charging operation. During drum discharge, the mixing blades 6, 7 convey the concrete from the drum mixing area to the drum discharge opening 5, and thus the concrete is forced through the passageway 12 defined by the outer periphery of the charging cone 10 and the wall of the rear drum section 3, and at this point is most susceptible to clogging which causes a slow and unsatisfactory discharge rate.

In the present invention, however, because the wall of the rear drum section 3 is parallel to the axis of the drum 1 instead of converging inwardly towards the drum axis as would be the case if this section of the drum conformed to the frusto-conical shape of the front drum section 2, there is no substantial opposition to the free and smooth discharge of the concrete as it passes through the passageway 12. Thus, I have found that a drum shaped as in drum 1, and merely by reason of this shape, has a discharge rate which is satisfactory for use on transit concrete mixers.

In addition to not opposing the discharge flow, the rear drum section 3 is necessarily wider than a tapering rear drum section of a traditional completely frusto-conical shaped drum of comparable size, and thus allows making the first coils of the spiraled blades 6, 7 slightly larger in height to give a larger pushing surface at the discharge the. capacity required-in: theadrurn, therate offldis'charge required'of. the drum,- and; also the numerous factors which may contribute to -drum leakage, astfon example,- whethen the-.concrete. is high. or lovwsl urnp; the usual inclines traversed by the transit mixenwhile traveling to thetjob site, etc. It. is therefore diflicultr to prescribe one ratio for. these lengths. fittingalla situations other thamto statethat! havetfoundithat. thezmostversatile .drum having the improveds. shape. hereindescribed is. obtained. when the length -.of -the; rear drum section. 3 is approximately onetenth. the length of: thetfrontdrumsectionl2', or as-thesea lengths. are representeda in. the drawing, the-line B one-tenth that. of line A.B'.'.

Itz-will be. understood: of course that, the invention: is notintendeda'to-be limitedrto thetratio'of 1:10 for the drum sections, or is it: to be limited totheexact: shape forthemixing-drum ,sections shown-herein, but that wid'e modifications can. betmade-in each:within.the invention as definedby. the claims.

Whatv is claimed is:

1. A. mixing. drum comprising" a. hollowfront drum: section: and. a hollow. rear drumtsection connected' to each other-and rotatableabout. its axis, aniendiopeninginrthe rear. drum section. for discharging the drum-contents,- and a plurality. oftaxially spiraledamixingtblades. eachof whichi originate in said:end;opening and extendacontinuously in-- wardly. therefrom .along the; interior: wall of said trear and: frontdrum sections,. said: front drum. section having a. Wide: base and sides tapering. inwardly: towards the drum axis in the direction of the rear drum section defining a substantially frusto-conical shaped mixing areai ofrrelativelyi largecapacity, and said: rear. drumsection being:-

substantially cylindrical in shape having sides parallel to the drum axis extending from the end of the tapering sides of said front drum section to the end discharge opening, whereby clogging in the materials flowing to the said end discharge opening is minimized.

2. A mixing drum comprising ahollow front drum section and a hollow rear drum section connected to each other; and rotatable; about its axis antend opepingin: the; rear ru ction? sq a li g rumi ements plurality of axially spiraledmixing blades each ofwhich originates in said end opening and extends continuously inwardly therefrom alongthe'interior wall o f' s and front drum sections, and a charging cone dlsp centrallyg; of; the; mixing blades in; said v end opening said front drum section having a wide base and sides tapering inwardly towards the drum axis in the direction of the rear drum section defining a substantially frusto-conical shaped mixing area of relatively large capacity, and said rear-drum section-being substantially cylindricalinshape having sides parallel to the drum axis extendingfor axial; length of said 'charging come from the'end of' -ther tapering sides of ifsaid front drumsection to the endedis charge opening, whereby clogging in the mater-ials flOVving between said charging cone and'theinterior wall 'of" saidrear -dx um section to the-said discharge opening. minimized- References Gited in the-fileof thispatent-f EEED STATES, PATENTS; 

